That's not enough information to reach a diagnosis, but when you add that a wrong light turns on with the intended one, there are two things to consider. Most commonly, check for a trailer wiring harness that is chewed up, often from rubbing on the ground when you go up a steep, sudden incline like a driveway entrance. This was also a real common problem caused in the '90s by a lot of trailer harnesses installed by U-Haul. They have three red leds to help you identify the circuits. I ran into a bunch of them with connectors that were melted and the leds were shorted.
This would also happen when an 1156 bulb with a single terminal was installed in place of the required 1157 bulb with two contacts. The single contact on the bulb straddled the two contacts in the socket, shorting the turn signal / brake light circuit to the tail light circuit. You should have the newer 3157 bulbs with the plastic bases, so this can't happen, and you have two separate bulbs for brakes and turn signals. Where you still can have a problem is with a bad ground wire that both sockets share. Current for one bulb can't get to ground directly to cause the bulb to be full brightness. Instead, it finds an alternate path through a different bulb, then over to that bulb on the other side of the vehicle, then to ground. Now you have the 12 volts split up between three bulbs instead of one so while they all might appear to be on, they will not be as bright as normal.
That condition of three bulbs in series when there's a bad ground also results in greatly decreased current flow. With older mechanical flashers, that current is insufficient to make it work, so it won't flash. Newer cars have electronic flashers that flash too fast to let you know there isn't enough current flow, which is normally caused by a burned-out signal bulb.
The first thing you have to explain is whether this problem started after the multifunction switch was replaced, or if you replaced the switch to try to solve this problem.
Saturday, November 8th, 2014 AT 11:12 PM